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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?

i even get this one. having more intake than exhaust is not only recommended via some of the links above. it prevents negative pressure in the attic from too much exhaust which would suck from the easiest source...that can be the house. other unsealed areas, you name it. from what i gather is the idea is to have enough soffit that the ridge exhaust can easily pull on the soffit. being right at 1:1 gives you no wiggle room if anything gets blocked. my own home is going to come in at 1.4:1 which should be open, breezy and prevent high humidity conditions up there.

i've been adding 50-100sq in of intake per day in my free time and i literally have watched the humidity meter drop a few % each day

He always preaches to aim high on the intake side. Intake air is more often overlooked or obstructed, creating an imbalance the other way. If there is too much exhaust, you just drive stack pressure and air loss from the envelope.

Intake air is also a bit more difficult to get right in most cases vs. just about anyone can easily add in additional ridge vent or box vents to make up for lack of exhaust air.

Most of the homes that I go into with persistent venting issue are lacking intake volume or have obstructed some aspect of it.

okay I can accept that one. Reason is more of a practical one due to the vast lack of attention to details of the construction industry in general. However you can also go overboard. If you pressurize the attic space you drive heated air in the summer into the conditioned space below. The ideal is one to one! And completely sealing the attic floor is far more critical than attic venting in most climate zones.

In post 29, I showed our (U.S.) codes are allowing for 50-60% soffit over exhaust, any more than that and you create the possibility of air in one soffit---out the soffit right next to it. No reason to go up if the resistance is less down below. Here is the idea: 10-15 % (or 55-58%) more soffit than exhaust is recommended here, pp. 615: http://books.google.com/books?id=Z8a...0vents&f=false

Many won't achieve those figures as WoW said, much easier than crawling at the soffits- especially for us old guys....There is not much research on the percentages ratio with test results, I'm still looking...

Gary

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If any ads are present below my answer or words underlined/colored, I do not condone/support/use the product or services listed/linked to, they are there without my consent.
17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?

okay I can accept that one. Reason is more of a practical one due to the vast lack of attention to details of the construction industry in general. However you can also go overboard. If you pressurize the attic space you drive heated air in the summer into the conditioned space below. The ideal is one to one! And completely sealing the attic floor is far more critical than attic venting in most climate zones.

Convection will probably always steer a negative pressure even the the presence of a slightly overbalanced intake:exhaust ratio.

Stack pressures during what the the more problematic venting seasons (winter) are already in effect in the home and pushing warm, moist air up into the attic.

In those cases I would always prefer a slightly overbalanced intake vs. exhaust if I am going to err on one side or the other.

Air sealing is first and foremost and that is why I mention it in nearly every discussion about ventilation. It will nearly always mitigate or completely eliminate the needs for modification.

well, it's been a little over a week since i did everything that was mentioned. couple cans of spray foam and hvac tape did wonders sealing the attic floor. had a couple really big home to attic vents, one being that bathroom vent, second being from the kitchen. the cutout for the exhaust vent had a good 3/8" all around going directly to the attic. that's on a...what...8" pipe so that's a good amount of air. anyway. with the gable closed down and sealing done along with a whopping 98 more 2.5" holes in the soffits {hole sawed 6-7 -2.5" holes in each soffit i chose} the air feels about the same up there as it does outside and get this...the mold is dying on its own. some areas that had grey splotches starting are either gone totally or shrinking. i microban'd the worst areas but the minor areas appear to be dying on their own with the food source cut off

Yeah - rounded up. But the resulting NET area is reduced significantly when an insect screen or louvers are added.

Glad your solution is working.

i figured it would be, i used the chicken wire style 22 by 3.5" slide in grills they had at lowes to cover the holes and aimed for a 1.5 to 1 intake to exhaust ratio just for this very reason.

which again, i'm glad you guys pointed out was the smart play. had i just read the instructions and went with 1:1 when the screens and any debris get factored in i would certainly have more exhaust than intake. great setup for a turbocharged car, not so much for an attic